The present invention generally relates to feedthrough devices, and more particularly relates to extending the operating life of an apparatus that incorporates a feedthrough device by extending the operating life of the feedthrough device itself.
Electrical feedthrough assemblies provide a conductive path extending between the interior of a hermetically sealed container and a point outside the container. Electrical medical devices such as biorhythm sensors, pressure sensors, and implantable medical devices (IMD""s) such as pulse generators and batteries often incorporate feedthrough assemblies. The conductive path comprises a conductive pin or other type of terminal that is electrically insulated from the container. Many feedthrough assemblies are known in the art, and typically include a ferrule, and an insulative material such as a glass or ceramic material, for positioning and insulating the pin within the ferrule. The reliability of the feedthrough assembly depends in large part on the durability of a hermetic seal between the various feedthrough assembly components. A hermetic seal is formed by heating and/or curing the insulating material, and may be strengthened by brazing the interfaces of the feedthrough assembly components using a brazing metal or alloy.
Feedthrough assemblies are subject to corrosion which can cause the seals to lose their hermeticity. When a feedthrough is functioning, the terminals are under continuous DC or AC bias. If the metal that brazes the glass/metal interface around the positive terminal is conductive, there is a likelihood that an anodic current density will be concentrated around the metal braze, causing the metal to corrode rapidly. In the case of a positive bias applied to the feedthrough pin, this is especially the case if the metal that forms the brazing is less passive (more conductive) than the pin. Moreover, there is a likelihood that the brazing around other glass/metal interfaces will be subject to corrosion as well. Corrosion of the metal brazing results in loss of hermeticity and the need for replacement of the feedthrough, or perhaps the entire device in which the feedthrough is incorporated.
In the case of batteries, organic electrolytes are a common cause of corrosion and cracking of both the insulating glass and the metal feedthrough components. Similar problems associated with corrosion are encountered with IMD""s having feedthrough terminals that come into contact with body fluids.
Accordingly, it is desirable to improve the durability of feedthrough devices incorporating metal brazing to provide or strengthen a hermetic seal by lessening or eliminating corrosion of the metal brazing. It is also desirable to provide an improved feedthrough device and a method for making the same. In addition, it is desirable to provide an electrical device that incorporates an improved feedthrough device. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.
A feedthrough assembly is provided for facilitating external electrical contact with an enclosed electrical circuit. The feedthrough assembly includes a ferrule, an insulating material contacting the ferrule, and a terminal extending through the ferrule and having first and second areas separated by an area contacting the insulating material. A brazing material contacts the insulating material and the terminal""s first area, and a conductive material covers the terminal""s second area. The presence of the corrosion resistant conductive material causes current density to be dispersed away from the brazing material.
A medical device is provided that incorporates a feedthrough assembly. The medical device includes an encasement, an electrical device disposed within the encasement, and the feedthrough assembly as described above. The feedthrough terminal is electrically coupled to the electrical device.
A method is provided for manufacturing a feedthrough assembly. The method includes the steps of covering a first area of a terminal with a conductive material, inserting the terminal through a ferrule, and surrounding an area of the terminal that is within the ferrule with an insulating material. A second area of the terminal and an adjacent region of the insulating material are then brazed with a brazing material. The brazing material is separated from the conductive material to thereby cause current density to be dispersed away from the brazing material.
A method is also provided for facilitating electrical contact with an electrical device disposed within a medical device having an encasement with an opening therein. The method comprises the steps of covering a first area of a terminal with a conductive material, inserting the terminal through a ferrule, and surrounding an area of the terminal that is within the ferrule with an insulating material. A second area of the terminal and an adjacent region of the insulating material are then brazed with a brazing material. The brazing material is separated from the conductive material to thereby cause current density to be dispersed away from the brazing material. The ferrule is then inserted into the encasement opening, and the terminal is electrically coupled to the electrical device.